All the coolant that flows out during a water pump replacement effectively drains coolant from the engine block, correct? So when mechanics say the coolant is replaced as well during a timing belt + water pump job, does this mean they also drain the radiator so you now have nearly 100% new coolant in the system? I've always wondered about this .

Every block is alittle different but basically it's drained at least to that level, some will remain.When you pop the hose off the WP the coolant is lost unless locking hose clamps are used and or the lost coolant is saved and returned to re-fill it.Thats pretty chintzy though.

When I replaced my water pump I drained the old coolant out by removing the lower radiator hose. Then coolant came pouring out of the block when I removed the pump. My engine has a block drain but I did not open it. There was not much left in the block anyway, it took right at the rated spec, I think it was about 2.5 gallons of 50/50 coolant to water to re-fill the cooling system. I used brand new coolant and water when I re-filled it.

If in fact the radiator was also drained, and not everyone does that automatically for various reasons, when the water pump was replaced then anywhere from about 60% to 80% of the coolant may have been drained.

The location of the water pump on the engine determines how much coolant is drained from the engine while changing the pump. Some engines have the water pump lower or higher on the engine than others, therefore more or less coolant is drained out of the engine and cooling system.

As for the radiator being drained, that depends upon a number of factors. One is access to the drain plug or petcock. In some vehicles it is next to impossible to get to, so the lower radiator hose is pulled instead and that is sometimes nearly as effective as draining from the drain plug. Other factors are how much time the mechanic has to do the job, how neat he is, how conscientious he is, what the shop protocol is, etc. In other words don't assume that the radiator was drained, and drained properly, in the course of replacing your water pump.

Even if the radiator was drained when the pump was changed there will still be old coolant left in the engine, and probably in the heater core and various hoses. The only way to get 100%, or even 95%, is to use a coolant change machine, which are often useless and I don't know if anyone still uses them anymore, or repeated cycles of drain, refill with water and running the engine, until the fluid drained out looks like straight water. For my cars I prefer the repeated drain and refills.

It's an arguable point as to whether or not removing 100% of the old coolant really makes a big difference. There are lots of cars on the road with way over a 100,000 miles that have had the cooling system serviced in a half...way manner that are still running fine.

If they made an honest attempt at draining the radiator and refilled with the right coolant you're probably OK.

All the coolant that flows out during a water pump replacement effectively drains coolant from the engine block, correct?

Depends on the engine.

Originally Posted By: mclasser

So when mechanics say the coolant is replaced as well during a timing belt + water pump job, does this mean they also drain the radiator

They drain the rad AND THE BLOCK.

On a Honda, if you pull the water pump without draining the block, a quart of coolant will pour all over the engine in the worst possible place once the pump is loose, and make a big mess. So you drain the block as well as the rad before pulling the pump. Once the block is drained, only a small dribble will escape when the water pump is removed.

Don't let ANYBODY tell you that you can change the coolant properly without draining the block. Doing so is a "fudge" performed by home mechanics who are trying to get out of doing a proper job.